You're missing an important thing. Darkcoin is, at a minimum, as anonymous as bitcoin. That's worst case scenario if we say darksend can be cracked. If not, it's more anonymous than bitcoin, probably way more, and only getting better. I think it's a great move from the owners.
The whole point of the existence of darkcoin is that it's a trustless solution. There are already bitcoin mixing services that use coinjoin. What is the point of making darkcoin when there are already coinjoin services? Because darkcoin is trustless, once it's open sourced. By suggesting it should be closed source is negating the point of darkcoin, requiring trust for a supposedly trustless solution.